Method of making ore briquettes



Jan. 3, 1967 R. T, JOHNSON METHOD OF MAKING ORE BRIQUETTES Filed Sept. 22, 1964 Off Gas F laid/zed Bed or Reducing Gas Hot Gas Specular Hematite L imestone 0 Percent, Reduction of Specular Hematite mtmautm 8 39395 mE3 393m M 5 0 H VJ N au/ R 0 I R I w A t torney Patented Jan. 3, 1967 3,295,952 METHOD OF MAKING ORE BRIQUETTES Roger T. Johnson, Monroeville, Pa., assignor to United States Steel Corporation, a corporation of Delaware Filed Sept. 22, 1964, Ser. No. 398,346 Claims. (Cl. 75-3) This invention relates to an improved method of briquetting specular hematite fines.

An earlier application of Brisse and Rohaus, Serial No. 271,938, filed April 10, 1963, now Patent No. 3,174,846, describes and claims a method of briquetting iron oxide fines with a bituminous coal binder. The iron oxide fines and preferably a flux are heated under oxidizing conditions to a temperature above the softening point of coal and thereafter mixed with low-temperature bituminous coal fines. The mixture contains about 5 to 15 percent coal and it reaches an apparent temperature of about 600 to 800 F. The mixture is briquetted immediately following the mixing step while its temperature remains in this range. I have observed that briquettes of specular hematite made by this method are not as satisfactory as briquettes of other types of iron ore. They have fair handling strength, but when heated to about 1900 F. in a simulated blast furnace test, they swell and become quite weak. The swelling is objectionable in a blast furnace, since it restricts upward flow of gases and descent of solids.

An object of my invention is to provide an improved method of briquetting specular hematite fines with a bituminous coal binder and largely overcoming the swelling problem.

A more specific object is to provide a method of briquetting specular hematite fines by a procedure similar to the Brisse and Rohaus method, but in which I heat the fines under reducing conditions and partially reduce the hematite before mixing them with coal fines, and in which I prevent reoxidation of the hematite.

In the drawing:

FIGURE 1 is a diagrammatic representation of apparatus suitable for performing my briquetting method; and

FIGURE 2 is a graph illustrating the beneficial effects my invention achieves.

According to my invention, I continuously feed minus 4 inch specular hematite fines and preferably a flux to a reducing chamber 10, as with a screw conveyor 12. I illustrate chamber as of the fluidized-bed type, although I could use other types, for example a rotary kiln. Hot reducing gas (for example hydrogen, carbon monoxide or mixtures thereof) enters chamber 10 through an inlet 13 in the bottom, and off-gas discharges through an outlet 14 in the top, as known in the art. In this manner I heat the hematite to a temperature usually of about 850 to 1050 F. and reduce it by about 15 to 30 percent, or preferably about 18 to 23 percent. This terminology means that I remove from the iron oxide present in the hematite 15 to 30 percent or 18 to 23 percent of the oxygen originally contained therein.

Heated particles continuously discharge from chamber 10 through an overflow 15 out of contact with air and go to a mixer 16, for example a pug mill. I also continuously introduce minus 8-mesh low-temperature bituminous coal fines to the mixer through an inlet 17. The partially reduced hematite particles, flux particles, and coal particles remain in the mixer long enough to form a uniformly dispersed mixture. The proportions are such that the mixture contains about 5 to 15 percent coal and preferably sufiicient flux that it is self-fluxing. The mixture has an apparent temperature of about 600 to 800 F. When the coal particles are at an ambient temperature of about 70 F. and the hematite and flux particles are heated to about 850 to 1050 F., the mixture reaches the proper temperature. When the coal particles are at a different temperature, I can make compensating adjustments in the temperature to which I heat the other particles.

The mixture goes directly and continuously from the mixer 16 out of contact with air to a briquetting press 18, illustrated as of the roll-type. The press compacts the particles into briquettes under a load of about 30,000 to 65,000 pounds per linear inch of effective roll width and thus forms them into pillow-shaped briquettes. The coal itself serves as a binder. Next I transfer the briquettes to a cooling shaft 19 where they cool to a maximum temperature of about 200 F. I show an oscillating conveyor 20, which receives briquettes from the press, and a bucket elevator 21, which lifts the briquettes from the discharge end of the conveyor to an inlet at the top of the shaft. Cooled briquettes discharge from the bottom of the shaft to a conveyor 22. The shaft inlet and outlet contain rotary valves 23 and 24 respectively to prevent escape of gases.

It is critical to the successful practice of my invention that I prevent the partially reduced hematite from reoxidizing. To cool the briquettes in shaft 19, I introduce a cool inert or reducing gas to the lower portion through an inlet 25, and discharge this gas along with entrained fines through an outlet 26 in the upper portion. If the cooling gas is a reducing gas, conveniently I can use olfgas from the cooler as reductant in chamber 10. In this way I return the entrained fines and also take advantage of the heat the gas receives in cooling thebriquettes, although it is necessary to raise the temperature of the gas to about 900 to 1100 F. before introducing it to the chamber. Conveyor 20 and bucket elevator 21 are suitably enclosed to prevent oxidation of the briquettes as they are transported from the press to the cooling shaft.

As a specific example to demonstrate my method, I made a series of briquettes which contain 73.2 percent minus 6-mesh specular hematite concentrate, about 20 percent minus IOO-mesh bituminous coal, and 6.8 percent minus IOO-mesh limestone. Prior to briquetting, I reduced various samples of the concentrate within the range of 0 to 23 percent, using hydrogen as the reductant. I pressed all the mixes at 650 F. and 20,000 pounds to form briquettes. I tested the briquettes under simulated blast furnace conditions (heated to 1900 F. in a tube through which a reducing gas is flowing). FIGURE 2, shows graphically the results of these tests. Briquettes in which the hematite was unreduced increased in volume about 23 percent. Briquettes in which the hematite was slightly reduced (up to about 8 percent) swelled even more. Briquettes in which the hematite was reduced 10 percent or more showed much less swelling. A volume increase of about 10 percent is the maximum that would not cause trouble in a blast furnace. Briquettes in which the hematite was reduced about 15 percent or more increased in volume less than 10 percent.

From the foregoing description it is seen that my invention aifords a simple effective method of briquetting specular hematite fines and overcoming the swelling problem. I am aware that it has been proposed previously to reduce ore fines preliminary to briquetting. However, the previous practice either was for the purpose of increasing the physical strength of the briquettes, and the ore was purposely reoxidized, or else the ore was reduced to a much higher degree, as in the production of sponge iron.

While I have shown and described only a single embodiment of my invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A method of briquetting specular hematite fines comprising heating the fines under reducing conditions to raise their temperature to the range of about 850 to 1050 F. and eifect about 15 to 30 percent partial reduction of the hematite, mixing low-temperature bituminous coal fines with the heated and partially reduced hematite fines to produce a uniformly dispersed mixture containing about 5 to 15 percent coal and having an apparent temperature in the range of about 600 to 800 F., compacting the mixture into briquettes directl following the mixing step and while it remains at a temperature in the latter range, the coal itself serving as a binder, and cooling the briquettes but preventing reoxidation of the hematite.

2. A method as defined in claim 1 in which the heating and reducing step is performed in a fluidized bed, and

the fiuidizing gas is selected from the group which consists of hydrogen, carbon monoxide and mixtures thereof heated to temperatures to 900 to 1000 F.

3. A method as defined in claim 1 in which suificient fluxing material is included With the hematite fines to produce self-fluxing briquettes.

4. A method as defined in claim 1 in which the briquettes are cooled in a shaft to which a cool reducing gas is introduced, and off-gas from said shaft is used in heating and reducing the hematite.

5. A method as defined in claim 1 which the partial reduction is about 18 to 23 percent.

No references cited.

BENJAMIN HENKIN, Primary Examiner. 

1. A METHOD OF BRIQUETTING SPECULAR HEMATITE FINES COMPRISING HEATING THE FINES UNDER REDUCING CONDITIONS TO RAISE THEIR TEMPERATURE TO THE RANGE OF ABOUT 850 TO 1050F. AND EFFECT ABOUT 15 TO 30 PERCENT PARTIAL REDUCTION OF THE HEMATITE, MIXING LOW-TEMPERATURE BITUMINOUS COAL FINES WITH THE HEATED AND PARTIALLY REDUCED HEMATITE FINES TO PRODUCE A UNIFORMLY DISPERSED MIXTURE CONTAINING ABOUT 5 TO 15 PERCENT COAL AND HAVING AN APPARENT TEMPERATURE IN THE RANGE OF ABOUT 600 TO 800F., COMPACTING THE MIXTURE INTO BRIQUETTES DIRECTLY FOLLOWING THE MIXING STEP AND WHILE IT REMAINS AT A TEMPERATURE IN THE LATTER RANGE, THE COAL ITSELF SERVING AS A BINDER, AND COOLING THE BRIQUETTES BUT PREVENTING REOXIDATION OF THE HEMATITE. 